WASHINGTON (Reuters) - The experimental unmanned jet that made aviation history by landing on an aircraft carrier this week detected a problem with its systems during a third touchdown attempt and diverted safely to a nearby airfield, Navy officials said on Thursday.

The aircraft refueled and then resumed testing, aiming to conduct a third landing, officials said. After a successful slingshot launch from the carrier's catapult, the X-47b lined up for its third carrier landing of the day.

"The aircraft had been catapulted, it was airborne, it was in the pattern ... it was on final approach about 4 miles out ... hook was down, gear was down," said Rear Admiral Mat Winter, the Navy program executive officer for unmanned aviation.

"As it's supposed to do, it continues to check the health and status of all its subsystems, and that's when it identified one of its navigation computer's anomalous behavior," Winter said.

The plane, which operates with little human intervention, climbed to a pre-set altitude and reported the problem to a controller on the aircraft carrier, who looked at the information and told the plane to divert to the pre-programmed airfield.

Salty Dog 502 flew to Wallops Island Air Field, on a barrier island along the Virginia coast, where it landed itself without further incident, officials said.

Winter downplayed the incident, saying anomalies are common in test aircraft subsystems. He said the Navy expected to continue testing the X-47B aboard the USS Bush next Monday, its next scheduled availability, probably using the second X-47B.

"Based on what we know right now, we fully expect to either operate Air Vehicle 1 or Air Vehicle 2 out to the ship to continue to finalize the objectives for X-47B," Winter said.

The program calls for the aircraft to do a minimum of three carrier landings, though the operators plan to do more if possible, officials have said.

Officials said workers on the program were going over the data from the aircraft to determine what caused the anomaly, which might be fixed simply by resetting the navigation computer.

Winter said a spare navigational computer could be swapped for the one that caused the problem, if needed, and the plane then flown back to Patuxent River Naval Air Station where it could be examined further.